Transcript for Battle Over Seat Space Heats Up With Another Mid-Air Fight

the skies, for the second time this week a passenger jet forced to land because of a mid-air fight in the cabin, once again, the battle over seat space and a flight attendant caught in the middle, ABC's David Kerley tells us this time it took air marshals to break it up. Reporter: The second air rage incident over reclining seats is now a federal case. Last night on the American airlines jet from Miami to Paris, a man fought with the passenger seated in front of him. He says because his legs hurt from diabetes. They tried the can calm the man. Air marshals broke their cover. The flight was diverted to Boston. This, just days after, a man on a united flight used these knee defenders to keep the seat in front of him from reclining. The woman in front was not happy, threw a cup in his face, leading to that flight being diverted too. A month ago, it was a Toronto S.W.A.T. Team bursting onto a jet to takeoff an unruly passenger. What's going on? Travelers today are more stressed than they've ever been before. When you finally do get to your seat, there's just less room than we've had in the past. Reporter: Last night's case, somewhat unique, because air marshals jumped in. The expert marksmen and highly trained air marshals work undercover. As I learned at their training center, their job is to take out a terrorist threat. But when it comes to an unruly passenger rather than a terrorist, the marshals on board have to make the call. We are tasked with protecting the flight deck, the flight crew, the passengers and then ourselves. Reporter: An increase in number of incidents involving unruly passengers and airlines have plans to pack even more of us into their jet liners.

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